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URDF joint element

#urdf   #joint  

Table of Content

URDF joint element#

joint element

Joint types#

  • fixed: All degrees of freedom are locked.
  • continuous: a continuous hinge joint that rotates around the axis and has no upper and lower limits.
  • revolute: a hinge joint that rotates along the axis and has a limited range specified by the upper and lower limits.
  • prismatic: a sliding joint that slides along the axis, and has a limited range specified by the upper and lower limits.
  • floating: this joint allows motion for all 6 degrees of freedom.
  • planar: this joint allows motion in a plane perpendicular to the axis.

Demo#

  • Simulate /joint_state topic with joint_state_publisher_gui
  • Launch and show it in rviz

urdf#

basic_joint.urdf
<?xml version="1.0" encoding="UTF-8"?>
<robot name="my_robot">
    <link name="world" />

    <joint name="fixed" type="fixed">
        <parent link="world" />
        <child link="link1" />
    </joint>

    <!-- Base Link -->
    <link name="link1">
        <visual>
            <origin xyz="0 0 0.5" rpy="0 0 0" />
            <geometry>
                <box size="0.1 0.1 1" />
            </geometry>
            <material name="Green">
                <color rgba="0 1.0 0 1.0" />
            </material>
        </visual>
    </link>

    <joint name="link12link2_joint" type="continuous">
        <parent link="link1" />
        <child link="link2" />
        <origin xyz="0 0.05 1" rpy="0 0 0" />
        <axis xyz="0 1 0" />
    </joint>

    <!-- Middle Link -->
    <link name="link2">
        <visual>
            <origin xyz="0 0.05 0.5" rpy="0 0 0" />
            <geometry>
                <box size="0.1 0.1 1" />
            </geometry>
            <material name="Red">
                <color rgba="1.0 0 0 1.0" />
            </material>
        </visual>
    </link>

</robot>

launch#

  • Run robot_state_publisher
  • Run joint_state_publisher_gui
urdf_link.launch.py
import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch_ros.actions import Node

URDF = "basic_joint.urdf"
PACKAGE = "gazebo_tutorial_pkg"


def generate_launch_description():
    ld = LaunchDescription()

    pkg = get_package_share_directory(PACKAGE)
    urdf = os.path.join(pkg, "urdf", URDF)
    with open(urdf, "r", encoding="utf-8") as f:
        robot_description = f.read()

    robot_state_publisher = Node(
        package="robot_state_publisher",
        executable="robot_state_publisher",
        name="robot_state_publisher",
        output="screen",
        parameters=[{"robot_description": robot_description}]
    )

    joint_state_publisher_node = Node(
        package="joint_state_publisher_gui",
        executable="joint_state_publisher_gui",
        name="joint_state_publisher_gui",
    )

    ld.add_action(robot_state_publisher)
    ld.add_action(joint_state_publisher_node)
    return ld

rviz#

run rviz
rviz2